The gene organization of a human proto-oncogene, c-fgr, is under investigation as a basis for understanding its normal functions and role in tumorigenesis. The cDNA library of human endothelial cells was screened by molecular hybridization using as a probe the tyrosine kinase portion (v-fgr) of the Gardner Rasheed feline sarcoma virus (GR-FeSV). Four unique clones of different sizes were isolated and the sequence of the longes one (1.5 kb) determined. The sequence showed a high degree of homology with v-fgr, v-yes and v-src oncogenes. It also revealed that the genomic sequence corresponding to this cDNA has a stop codon 36 bp downstream to the common recombination site of v-fgr and v-yes. The cDNA libraries from human cells which produce c-fgr mRNA in large quantities are under construction.